The process known as universal beam rolling starts with an initial section (1) of rectangular cross section (FIG. 1) and is characterized by having two distinct steps. In the first non-universal step, the initial section (1) is rolled in one or more two-high stands (called the "breakdown" mill) through a plurality of passes made in closed or open grooves which convert the initial section into a partially manufactured section (2) called the "dogbone" (FIG. 1). In the second universal step, the dogbone (2) is rolled through a plurality of passes in open edging and universal grooves which convert it into a finished H or I-beam section (3) (FIG. 1). See Iron and Steel Engineer, May, 1970, page 76.
The process described above has two major disadvantages. The first of these is the necessity of forming the dogbone (2), during the first step, in closed grooves and to turn-over the bar through 90.degree. during the rolling. This disadvantage considerably reduces the rolling speed and causes high wear and tear on the rolls. The second disadvantage is the requirement that the thickness ["E" in FIG. 1] of the initial section (1) exceed the height [h' in FIG. 1] of the dogbone (2) and the flange height ["H" FIG. 1] of the finished beam. This disadvantage of universal beam rolling was not as critical when initial sections (1) were produced by ingot-fed blooming mills which could produce initial sections of the various dimensions required by the beam mill rolling program. However, widespread manufacture of initial sections by continuous casting has caused this second disadvantage to assume increased significance.
In its present state of technological development and operative earning capacity, continuous casting does not always allow casting a bloom of sufficient bulk for a blooming mill to be able to convert it into as many initial sections of variable dimensions as are required by the beam mill rolling program. Moreover, use of a blooming mill reduces the earning capacity otherwise available from continuous casting.
To remedy the above mentioned disadvantages of universal beam rolling, Soviet author's Certificate 174.160 issued Aug. 27, 1965 recommends rolling continuous cast slabs in a reversible universal stand to make the dogbones needed for producing beams with very high webs. This reference, however, does not disclose the procedure for applying said recommendation, nor does said recommendation eliminate the second disadvantage of the known universal beam rolling process. The thickness E of the slab would still have to be greater than or equal to the dogbone flange height h' and the finished beam section flange height height H.
German Patent Specification No. 744,683 issued Jan. 22, 1944 advocates cold universal rolling of a small-sized rectangular initial section for producing curtain rods or toy train rails. However, this reference also fails to explain the procedure and does not hint or suggest any means for eliminating the second disadvantage discussed above. Referring to FIGS. 1 and 5 of German Pat. No. 744,683, a comparison of the thickness of the initial section (FIG. 1) with that of the finished section flange height (FIG. 5) show that the initial section thickness exceeds the finished flange height. Therefore, the second disadvantage of the universal beam rolling process remains unresolved by the teaching of this reference.
French Patent Specification Nos. 2,346,063 and 2,464,759 suggest thrusting an initial section between vertical rollers or rolling it between horizontal rolls to produce a dogbone of flange height h' greater than the initial section thickness E. Though one of the objects of the French patents is similar to that of the present invention, the procedures set forth in them are entirely different.